C Program not opening Serial on Arduino Mega - c

Question

I have a C program (win32 api) which communicates to my Arduino Mega via serial (USB).
I can communicate to the Arduino fine via the IDE's serial monitor.
If I plug in my Arduino and run the C program, the port does not seem to be opened properly and there is no communication.
In this case, if I open the serial monitor from Arduino's IDE (or another serial program) and then close it again, the C program then works perfectly.
Here is my port code from the C program (in this example it is passed 5 as this is the port the Arduino is using):
CSerialPort.h:
#pragma once
#include <Windows.h>
#define CP_BAUD_RATE_1200 CBR_1200
#define CP_BAUD_RATE_9600 CBR_9600
#define CP_BAUD_RATE_1155 CBR_1155
#define CP_BAUD_RATE_4800 CBR_4800
#define CP_BAUD_RATE_19200 CBR_19200
#define CP_DATA_BITS_5 5
#define CP_DATA_BITS_6 6
#define CP_DATA_BITS_7 7
#define CP_DATA_BITS_8 8
#define CP_STOP_BITS_ONE ONESTOPBIT
#define CP_STOP_BITS_TWO TWOSTOPBITS
#define CP_STOP_BITS_ONE_AND_HALF ONE5STOPBITS
#define CP_PARITY_NOPARITY NOPARITY
#define CP_PARITY_ODD ODDPARITY
#define CP_PARITY_EVEN EVENPARITY
#define CP_PARITY_MARK MARKPARITY
#define CP_PARITY_SPACE SPACEPARITY
typedef HANDLE PORT;
PORT OpenPort(int idx);
void ClosePort(PORT com_port);
int SetPortBaudRate(PORT com_port, int rate);
int SetPortDataBits(PORT com_port, int databits);
int SetPortStopBits(PORT com_port, int stopbits);
int SetPortParity(PORT com_port, int parity);
int GetPortBaudRate(PORT com_port);
int GetPortDataBits(PORT com_port);
int GetPortStopBits(PORT com_port);
int GetPortParity(PORT com_port);
int SendData(PORT com_port,const char * data);
int ReciveData(PORT com_port, char * databuffer,int bufferlen);
CSerialPort.c
#include "CSerialPort.h"
#include <time.h>
PORT OpenPort(int idx)
{
HANDLE hComm;
TCHAR comname[100];
wsprintf(comname, TEXT("\\\\.\\COM%d"), idx);
hComm = CreateFile(comname, //port name
GENERIC_READ | GENERIC_WRITE, //Read/Write
0, // No Sharing
NULL, // No Security
OPEN_EXISTING,// Open existing port only
0, // Non Overlapped I/O
NULL); // Null for Comm Devices
if (hComm == INVALID_HANDLE_VALUE)
return NULL;
COMMTIMEOUTS timeouts = { 0 };
timeouts.ReadIntervalTimeout = 50;
timeouts.ReadTotalTimeoutConstant = 50;
timeouts.ReadTotalTimeoutMultiplier = 10;
timeouts.WriteTotalTimeoutConstant = 50;
timeouts.WriteTotalTimeoutMultiplier = 10;
if (SetCommTimeouts(hComm, &timeouts) == FALSE)
return NULL;
if (SetCommMask(hComm, EV_RXCHAR) == FALSE)
return NULL;
return hComm;
}
void ClosePort(PORT com_port)
{
CloseHandle(com_port);
}
int SetPortBaudRate(PORT com_port, int rate)
{
DCB dcbSerialParams = { 0 };
BOOL Status;
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
Status = GetCommState(com_port, &dcbSerialParams);
if (Status == FALSE)
printf("FALSE BAUD STATE");
return FALSE;
dcbSerialParams.BaudRate = rate;
Status = SetCommState(com_port, &dcbSerialParams);
return Status;
}
int SetPortDataBits(PORT com_port, int bits)
{
DCB dcbSerialParams = { 0 };
BOOL Status;
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
Status = GetCommState(com_port, &dcbSerialParams);
if (Status == FALSE)
printf("FALSE DATABITS STATE");
return FALSE;
dcbSerialParams.ByteSize = bits;
Status = SetCommState(com_port, &dcbSerialParams);
return Status;
}
int SetPortStopBits(PORT com_port, int bits)
{
DCB dcbSerialParams = { 0 };
BOOL Status;
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
Status = GetCommState(com_port, &dcbSerialParams);
if (Status == FALSE)
printf("FALSE STOP STATE");
return FALSE;
dcbSerialParams.StopBits = bits;
Status = SetCommState(com_port, &dcbSerialParams);
return Status;
}
int SetPortParity(PORT com_port, int parity)
{
DCB dcbSerialParams = { 0 };
BOOL Status;
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
Status = GetCommState(com_port, &dcbSerialParams);
if (Status == FALSE)
printf("FALSE PARITY STATE");
return FALSE;
dcbSerialParams.Parity = parity;
Status = SetCommState(com_port, &dcbSerialParams);
return Status;
}
int GetPortBaudRate(PORT com_port)
{
DCB dcbSerialParams = { 0 };
BOOL Status;
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
Status = GetCommState(com_port, &dcbSerialParams);
if (Status == FALSE)
return -1;
return dcbSerialParams.BaudRate;
}
int GetPortDataBits(PORT com_port) {
DCB dcbSerialParams = { 0 };
BOOL Status;
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
Status = GetCommState(com_port, &dcbSerialParams);
if (Status == FALSE)
return -1;
return dcbSerialParams.ByteSize;
}
int GetPortStopBits(PORT com_port) {
DCB dcbSerialParams = { 0 };
BOOL Status;
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
Status = GetCommState(com_port, &dcbSerialParams);
if (Status == FALSE)
return -1;
return dcbSerialParams.StopBits;
}
int GetPortParity(PORT com_port) {
DCB dcbSerialParams = { 0 };
BOOL Status;
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
Status = GetCommState(com_port, &dcbSerialParams);
if (Status == FALSE)
return -1;
return dcbSerialParams.Parity;
}
int SendData(PORT com_port, const char * data)
{
DWORD dNoOFBytestoWrite = strlen(data);
DWORD dNoOfBytesWritten;
BOOL Status = WriteFile(com_port,
data,
dNoOFBytestoWrite,
&dNoOfBytesWritten,
NULL);
if (Status == FALSE)
return -1;
return dNoOfBytesWritten;
}
int ReciveData(PORT com_port, char * data, int len)
{
DWORD dwEventMask;
DWORD NoBytesRead;
BOOL Status = WaitCommEvent(com_port, &dwEventMask, NULL);
if (Status == FALSE) {
return FALSE;
}
Status = ReadFile(com_port, data, len, &NoBytesRead, NULL);
data[NoBytesRead] = 0;
if (Status == FALSE) {
return FALSE;
}
return TRUE;
}
Test Code:
#include "CSerialPort.h"
#include <stdio.h>
#include <windows.h>
#include <stdlib.h>
bool sendComms(char * msgSndPtr, int portNum)
{
auto p1 = OpenPort(portNum);
SetPortBaudRate(p1, CP_BAUD_RATE_9600);
SetPortDataBits(p1, CP_DATA_BITS_8);
SetPortStopBits(p1, CP_STOP_BITS_ONE);
SetPortParity(p1, CP_PARITY_NOPARITY);
SendData(p1, msgSndPtr);
ClosePort(p1);
printf("%s sent.\n", msgSndPtr); //debug
//strcpy(msgSndPtr,"");
return 1;
}
bool receiveComms(char * msgRecPtr, int portNum)
{
bool status = 0;
strcpy(msgRecPtr,"");
SetPortBaudRate(portNum, CP_BAUD_RATE_9600);
SetPortDataBits(portNum, CP_DATA_BITS_8);
SetPortStopBits(portNum, CP_STOP_BITS_ONE);
SetPortParity(portNum, CP_PARITY_NOPARITY);
auto p1 = OpenPort(portNum);
status = ReciveData(p1, msgRecPtr, 50);
ClosePort(p1);
if (!status) //if nothing is received, cancel out and show error
{
return 0;
}
else
{
printf("%s received.\n", msgRecPtr); //debug
return 1;
}
}
void main()
{
char msgRec[50];
char * msgRecPtr = msgRec;
char msgSnd[50];
char * msgSndPtr = msgSnd;
while (!(strcmp("end",msgRecPtr)))
{
sendComms(msgSndPtr, 5);
receiveComms(msgRecPtr, 5);
printf("sent: %s\n, msgSndPtr);
printf("received: %s\n, msgRecPtr);
}
}
The arduino code:
int i = 0;
void setup()
{
// Initiate Serial
Serial.begin(9600);
while (!Serial) ; // wait for serial port to connect. Needed for native USB
Serial.println("serial ready");
}
void loop()
{
Serial.println("testing comms");
i++
delay (150);
if (i == 10) {
Serial.println("end");
}
}
If anyone has had this problem using win32 or knows how the Serial Monitor opens it's port, that would be very helpful.
Edit: just to clarify, once the port has been opened once successfully (by any program apart from my C program), my C program then works fine and can open/close the port successfully until the next power cycle.
Thanks

Answer 1

I have fixed your code!
The major errors were:
Incorrect use of COM port number where a handle was required
Closing the port after sending data and before receiving response which flush input buffer
Almost no error check which prohibed to know what was wrong
In the test code, the main loop was incorrect. No data was sent and breaking the loop when "end" was received was wrong.
I moved COM port parametrization once after opening the port (could be inside OpenPort as well).
The way you handle receive is related to the communication protocol you define. I have not touched that part. If it would be my software, I would design the protocol as a line oriented protocol that is each message sent and received would be in the form of lines terminated by a CRLF pair. Receiving can then be in a loop, cumulating all characters until the end of line is found.
Here after the fixed source code. There are still plenty of romm for enhancement.
Test code:
#include "CSerialPort.h"
#include <stdio.h>
#include <windows.h>
#include <stdlib.h>
bool SetComParameters(PORT comPort, int rate, int dataBits, int stopBits, int parity)
{
if (!SetPortBaudRate(comPort, CP_BAUD_RATE_9600)) {
fprintf(stderr, "Unable to set baudrate\n");
return 0;
}
if (!SetPortDataBits(comPort, CP_DATA_BITS_8)) {
fprintf(stderr, "Unable to set data bits\n");
return 0;
}
if (!SetPortStopBits(comPort, CP_STOP_BITS_ONE)) {
fprintf(stderr, "Unable to set stop bits\n");
return 0;
}
if (!SetPortParity(comPort, CP_PARITY_NOPARITY)) {
fprintf(stderr, "Unable to set parity\n");
return 0;
}
return 1;
}
bool sendComms(char* msgSndPtr, PORT comPort)
{
SendData(comPort, msgSndPtr);
return 1;
}
bool receiveComms(char* msgRecPtr, PORT comPort)
{
bool status = 0;
strcpy(msgRecPtr, "");
status = ReceiveData(comPort, msgRecPtr, 50);
return status;
}
void main()
{
char msgRec[50];
char* msgRecPtr = msgRec;
char msgSnd[50];
char* msgSndPtr = msgSnd;
int portNum = 1;
PORT com_port = OpenPort(portNum);
if (com_port == NULL) {
fprintf(stderr, "Unable to open COM%d\n", portNum);
return;
}
if (!SetComParameters(com_port, CP_BAUD_RATE_9600, CP_DATA_BITS_8, CP_STOP_BITS_ONE, CP_PARITY_NOPARITY)) {
fprintf(stderr, "Error setting parameters\n");
return;
}
do { // FPiette use of do/while instead of while loop
strcpy(msgSnd, "Hello\r\n");
if (!sendComms(msgSndPtr, com_port)) {
fprintf(stderr, "sendComs failed\n");
break;
}
printf("sent: %s\n", msgSndPtr);
if (!receiveComms(msgRecPtr, com_port)) {
fprintf(stderr, "receiveComms failed\n");
break;
}
printf("received: %s\n", msgRecPtr);
} while (strcmp("end", msgRecPtr));
ClosePort(&com_port);
printf("Done.\n");
}
CSerialPort.c:
#include <stdio.h>
#include "CSerialPort.h"
#include <time.h>
PORT OpenPort(int idx)
{
HANDLE hComm;
TCHAR comname[100];
wsprintf(comname, TEXT("\\\\.\\COM%d"), idx);
hComm = CreateFile(comname, //port name
GENERIC_READ | GENERIC_WRITE, //Read/Write
0, // No Sharing
NULL, // No Security
OPEN_EXISTING,// Open existing port only
0, // Non Overlapped I/O
NULL); // Null for Comm Devices
if (hComm == INVALID_HANDLE_VALUE)
return NULL;
COMMTIMEOUTS timeouts = { 0 };
timeouts.ReadIntervalTimeout = 50;
timeouts.ReadTotalTimeoutConstant = 50;
timeouts.ReadTotalTimeoutMultiplier = 10;
timeouts.WriteTotalTimeoutConstant = 50;
timeouts.WriteTotalTimeoutMultiplier = 10;
if (SetCommTimeouts(hComm, &timeouts) == FALSE)
return NULL;
if (SetCommMask(hComm, EV_RXCHAR) == FALSE)
return NULL;
return hComm;
}
void ClosePort(PORT* com_port)
{
if (com_port && *com_port) {
CloseHandle(*com_port);
*com_port = NULL;
}
}
int SetPortBaudRate(PORT com_port, int rate)
{
DCB dcbSerialParams = { 0 };
BOOL Status;
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
Status = GetCommState(com_port, &dcbSerialParams);
if (Status == FALSE)
return FALSE;
dcbSerialParams.BaudRate = rate;
Status = SetCommState(com_port, &dcbSerialParams);
return Status;
}
int SetPortDataBits(PORT com_port, int bits)
{
DCB dcbSerialParams = { 0 };
BOOL Status;
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
Status = GetCommState(com_port, &dcbSerialParams);
if (Status == FALSE)
return FALSE;
dcbSerialParams.ByteSize = bits;
Status = SetCommState(com_port, &dcbSerialParams);
return Status;
}
int SetPortStopBits(PORT com_port, int bits)
{
DCB dcbSerialParams = { 0 };
BOOL Status;
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
Status = GetCommState(com_port, &dcbSerialParams);
if (Status == FALSE)
return FALSE;
dcbSerialParams.StopBits = bits;
Status = SetCommState(com_port, &dcbSerialParams);
return Status;
}
int SetPortParity(PORT com_port, int parity)
{
DCB dcbSerialParams = { 0 };
BOOL Status;
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
Status = GetCommState(com_port, &dcbSerialParams);
if (Status == FALSE)
return FALSE;
dcbSerialParams.Parity = parity;
Status = SetCommState(com_port, &dcbSerialParams);
return Status;
}
int GetPortBaudRate(PORT com_port)
{
DCB dcbSerialParams = { 0 };
BOOL Status;
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
Status = GetCommState(com_port, &dcbSerialParams);
if (Status == FALSE)
return -1;
return dcbSerialParams.BaudRate;
}
int GetPortDataBits(PORT com_port) {
DCB dcbSerialParams = { 0 };
BOOL Status;
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
Status = GetCommState(com_port, &dcbSerialParams);
if (Status == FALSE)
return -1;
return dcbSerialParams.ByteSize;
}
int GetPortStopBits(PORT com_port) {
DCB dcbSerialParams = { 0 };
BOOL Status;
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
Status = GetCommState(com_port, &dcbSerialParams);
if (Status == FALSE)
return -1;
return dcbSerialParams.StopBits;
}
int GetPortParity(PORT com_port) {
DCB dcbSerialParams = { 0 };
BOOL Status;
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
Status = GetCommState(com_port, &dcbSerialParams);
if (Status == FALSE)
return -1;
return dcbSerialParams.Parity;
}
int SendData(PORT com_port, const char* data)
{
DWORD dNoOFBytestoWrite = strlen(data);
DWORD dNoOfBytesWritten;
BOOL Status = WriteFile(com_port,
data,
dNoOFBytestoWrite,
&dNoOfBytesWritten,
NULL);
if (Status == FALSE)
return -1;
return dNoOfBytesWritten;
}
int ReceiveData(PORT com_port, char* data, int len)
{
DWORD dwEventMask = 0;
DWORD NoBytesRead = 0;
BOOL Status = WaitCommEvent(com_port, &dwEventMask, NULL);
if (Status == FALSE)
return FALSE;
Status = ReadFile(com_port, data, len, &NoBytesRead, NULL);
if (Status == FALSE)
return FALSE;
data[NoBytesRead] = 0;
return TRUE;
}
CSerialPort.h:
#pragma once
#include <Windows.h>
#define CP_BAUD_RATE_1200 CBR_1200
#define CP_BAUD_RATE_9600 CBR_9600
#define CP_BAUD_RATE_1155 CBR_1155
#define CP_BAUD_RATE_4800 CBR_4800
#define CP_BAUD_RATE_19200 CBR_19200
#define CP_DATA_BITS_5 5
#define CP_DATA_BITS_6 6
#define CP_DATA_BITS_7 7
#define CP_DATA_BITS_8 8
#define CP_STOP_BITS_ONE ONESTOPBIT
#define CP_STOP_BITS_TWO TWOSTOPBITS
#define CP_STOP_BITS_ONE_AND_HALF ONE5STOPBITS
#define CP_PARITY_NOPARITY NOPARITY
#define CP_PARITY_ODD ODDPARITY
#define CP_PARITY_EVEN EVENPARITY
#define CP_PARITY_MARK MARKPARITY
#define CP_PARITY_SPACE SPACEPARITY
#define bool BOOL
typedef HANDLE PORT;
PORT OpenPort(int idx);
void ClosePort(PORT* com_port);
int SetPortBaudRate(PORT com_port, int rate);
int SetPortDataBits(PORT com_port, int databits);
int SetPortStopBits(PORT com_port, int stopbits);
int SetPortParity(PORT com_port, int parity);
int GetPortBaudRate(PORT com_port);
int GetPortDataBits(PORT com_port);
int GetPortStopBits(PORT com_port);
int GetPortParity(PORT com_port);
int SendData(PORT com_port, const char* data);
int ReceiveData(PORT com_port, char* databuffer, int bufferlen);